1. Field of the Invention
The present invention relates to a surface inspection apparatus for inspecting a surface of a wafer or the like in a process of manufacturing an IC chip, a liquid crystal display panel and so on.
2. Related Background Art
The IC chip and the liquid crystal display device panel are constructed by stacking a variety of different circuit patterns in a multi-layered structure on a wafer surface or the like. These circuit patterns are formed in a way that stacks the patterns layer by layer on the wafer by making use of a photolithography process and others. When forming these circuit patterns, if there are defects such as a scatter in thickness of a layer of resist for forming the circuit pattern, a flaw and so forth, this leads to an ill-manufactured product like the IC chip to be manufactured, and hence it is of much importance to inspect the surface in the manufacturing process.
The surface of the wafer or the like has hitherto been inspected by irradiating the wafer surface with a variety of illumination light from a variety of angles, wherein an observer directly visually observes the surface in a way that rotates or sways the inspection target wafer. Over the recent years, there has increasingly been a demand for automating the surface inspection in order to minimize a scatter in quality of the inspection, save a labor for the inspection and speed up the inspection. What was proposed under such circumstances, as disclosed in, for example, Japanese Patent Application Laid-Open Publication No.2000-28535, is a surface inspection apparatus, wherein the inspection target wafer surface is irradiated with use-for-inspection illumination radiation or light emitted from an illumination optical system, an imaging device receives regularly reflected radiation or light from the wafer surface and picks up an image of the wafer surface, and the apparatus inspects the wafer surface for a defect like a flaw and so forth by processing an image signal of the thus picked-up image.
By the way, according to this type of surface inspection apparatus, it is judged from an intensity of the regularly reflected radiation from the wafer surface whether the wafer surface is defective or not. The IC chip or the like provided on the wafer surface is formed by stacking repetitive patterns having fine pitches. When the wafer surface is irradiated with the use-for-inspection illumination radiation, there outgoes diffracted radiation corresponding to the repetitive pattern pitches. Therefore, the regularly reflected radiation decreases corresponding to an occurrence of the diffracted radiation, and the imaging device picks up the image of the wafer surface with an intensity corresponding to the thus decreased regularly reflected radiation.
In this case, if the pattern on the wafer surface is normal, the image based on the regularly reflected radiation containing the decrease in intensity that corresponds to the diffracted radiation occurred, is picked up. For instance, however, if the defect such as a defocus or the like occurs in the photolithography process for creating the pattern, as an intensity of the diffracted radiation from this defective portion is different from that of the diffracted radiation from a portion having a normal pattern, so is the intensity of the regularly reflected radiation. Then, in the surface inspection apparatus, the signal processing of the image picked up by the imaging device is executed, and it is checked whether there exists a portion exhibiting a different intensity of the regularly reflected radiation from a radiation intensity of the image of the normal pattern, thereby inspecting the surface for the defect caused by the defocus.
As explained above, according to the surface inspection apparatus using the regularly reflected radiation, it is required that not only the regularly reflected radiation but also the diffracted radiation be occurred from the use-for-inspection illumination radiation with which the pattern on the wafer surface is irradiated. The regularly reflected radiation from the wafer surface are, however, obtained normally from any angles. In contrast, the diffracted radiation occurs depending on a pattern pitch on the wafer surface, and an incident angle and a wavelength of the illumination radiation. The diffracted radiation cannot always be generated effectively at all times, and a problem is that the effective surface inspection cannot be attained as the case may be. Particularly when the pattern pitch is small, there arises the problem in which the diffracted radiation do not occur, and the effective surface inspection is hard to perform.
It is a primary object of the present invention, which was devised to obviate the problems described above, to provide a surface inspection apparatus capable of detecting, in the case of inspecting a wafer surface formed with a periodically repeated pattern, an image of the surface of the inspection target object on the basis of regularly reflected radiation or light from the surface of this inspection target object and thus inspecting the surface for a defect from a luminance of this image efficiently and simply.
To accomplish the above object, according to one aspect of the present invention, a surface inspection apparatus comprises an illumination optical system for irradiating an inspection target object having its surface formed with a periodically repeated pattern with illumination radiation or light for inspection, a converging optical system for converging regularly reflected radiation from the inspection target object, and an imaging device for detecting an image of the inspection target object by receiving the regularly reflected radiation or light converged by the converging optical system. The surface inspection apparatus inspects the surface of the inspection target object on the basis of the image of the inspection target object that is detected by the imaging device and an incident angle i and a wavelength xcex of the use-for-inspection illumination radiation or light with which the illumination optical system irradiates the inspection target object are set to satisfy the following formula:
xcex/(sin i+1)xe2x89xa6pxe2x80x83xe2x80x83(1)
where p is a pattern repetitive pitch.
If the incident angle i and the wavelength xcex of the use-for-inspection illumination radiation is set to satisfy the above formula (1) with respect to the repetitive pitch p of the pattern formed on the surface of the inspection target object, when the pattern is irradiated with the use-for-inspection illumination radiation, diffracted radiation invariably outgoes from the pattern. It is therefore feasible to effectively easily inspect the surface of the inspection target object on the basis of an intensity of the regularly reflected radiation or light.
The surface inspection apparatus may preferably further comprise a wavelength selection unit for restricting a wavelength band of the use-for-inspection illumination radiation in order to obtain the use-for-inspection illumination radiation having the wavelength xcex satisfying the formula (1).
The illumination optical system may preferably have a discharge radiation or light source for emitting line spectrums. An inspection efficiency is enhanced by using the discharge radiation or light source having these line spectrums, i.e., an intensive output.
The illumination optical system may preferably have a radiation or light source for supplying ultraviolet rays of which a wavelength is equal to 400 nm or smaller, and at least the illumination optical system may be disposed in an inert gas atmosphere or in a vacuum. In the case of using the radiation or light source for supplying the ultraviolet-rays having the wavelength of 400 nm or smaller as the radiation or light source of the illumination radiation for inspection, the diffracted radiation can be generated effectively from the pattern having an extremely small pitch. Further, though the ultraviolet-rays react to substances in the air with the result that the substances might adhere to the lens to frost the illumination system, this problem can be restrained from arising by disposing the illumination optical system in the inert gas atmosphere or in the vacuum.
According to the present invention the contrivance is that the incident angle i and the wavelength xcex of the use-for-inspection illumination radiation with which the illumination optical system irradiates the inspection target object are set to satisfy the above formula (1). Hence, when the pattern is irradiated with the use-for-inspection illumination radiation, diffracted radiation invariably outgoes from the pattern, and it is possible to effectively easily inspect the surface of the inspection target object on the basis of the intensity of the regularly reflected radiation.
Moreover, the surface inspection apparatus may preferably further comprise an image processing inspection device for obtaining an image of the surface of the inspection target object by processing an image signal given from the imaging device, and inspecting the surface of the inspection target object for its defect on the basis of the surface image. This makes it possible to easily obtain the auto surface inspection apparatus for automatically detecting the intensity of the regularly reflected radiation.